OBJECTIVE: To understand development and usage of vocal communication. RESULTS We have documented "babbling" in infant pygmy marmosets finding parallels between babbling in marmosets and that of human infants and are continuing research on babbling to determine whether and how call structure changes through babbling and how older infants that have been weaned might use babbling instrumentally. We are studying how pygmy marmoset and cotton-top tamarin infants use vocalizations appropriately. While young monkeys produce these vocalizations at an early age, it is several months before they begin to use them appropriately, and some vocalizations are not used appropriately until animals are breeding adults. We have presented families of cotton-top tamarins with familiar preferred foods, a familiar food made toxic by the addition of pepper and an unfamiliar food. The first animal to taste a preferred but now toxic food, head shakes and rubs it mouth on a branch. From these involuntary reactions other group members avoided this highly preferred food for three weeks after one animal tasted the food. In families with young infants however, the adult who first tasted the food gave infant-directed alarm calls to infants that had approached the food. In subsequent trials the infants no longer approached. The use of specific voluntary signals to communicate about toxic food to infants, but not to older group members suggests a form of "teaching" that has not been seen in other species of monkeys. FUTURE DIRECTIONS We will complete studies on how calls are used appropriately by pygmy marmosets and cotton-top tamarins. We will follow up several questions from our babbling studies do marmosets show an improvement in call production with age and amount of babbling? Do monkeys use babbling to signal a more infantile or subordinate status to gain priority of access to resources when they are older? We will replicate the study with toxic food.